[R] Maximum # of DLLs reached, or, how to clean up after yourself?

Jeff Newmiller jdnewmil at dcn.davis.ca.us
Wed Sep 14 15:41:06 CEST 2016

I never detach packages. I rarely load more than 6 or 7 packages directly before restarting R. I frequently re-run my scripts in new R sessions to confirm reproducibility. 
Sent from my phone. Please excuse my brevity.

On September 14, 2016 1:49:55 AM PDT, Alexander Shenkin <ashenkin at ufl.edu> wrote:
>Hi Henrik,
>Thanks for your reply.  I didn't realize that floating DLLs were an 
>issue (good to know).  My query is actually a bit more basic.  I'm 
>actually wondering how folks manage their loading and unloading of 
>packages when calling scripts within scripts.
>Quick example:
>	library(package1)
>	source("script2.r")
>	# do stuff reliant on package1
>	detach("package:package1", unload=TRUE)
>	library(package1)
>	library(package2)
>	# do stuff reliant on package1 and package2
>	detach("package:package1", unload=TRUE)
>	detach("package:package2", unload=TRUE)
>Script2 breaks Script1 by unloading package1 (though unloading package2
>is ok).  I will have to test whether each package is loaded in Script2 
>before loading it, and use that list when unloading at the end of the 
>Script2.  *Unless there's a better way to do it* (which is my question
>is there?).  I'm possibly just pushing the whole procedural scripting 
>thing too far, but I also think that this likely isn't uncommon in R.
>Any thoughts greatly appreciated!
>On 9/13/2016 7:23 PM, Henrik Bengtsson wrote:
>> In R.utils (>= 2.4.0), which I hope to submitted to CRAN today or
>> tomorrow, you can simply call:
>>    R.utils::gcDLLs()
>> It will look at base::getLoadedDLLs() and its content and compare to
>> loadedNamespaces() and unregister any "stray" DLLs that remain after
>> corresponding packages have been unloaded.
>> Until the new version is on CRAN, you can install it via
>> or alternatively just source() the source file:
>> (this might be better suited for R-devel; feel free to move it there)
>> As far as I understand the problem, running into this error / limit
>> _not_ the fault of the user.  Instead, I'd argue that it is the
>> responsibility of package developers to make sure to unregister any
>> registered DLLs of theirs when the package is unloaded.  A developer
>> can do this by adding the following to their package:
>> .onUnload <- function(libpath) {
>>     library.dynam.unload(utils::packageName(), libpath)
>>  }
>> That should be all - then the DLL will be unloaded as soon as the
>> package is unloaded.
>> I would like to suggest that 'R CMD check' would include a check that
>> asserts when a package is unloaded it does not leave any registered
>> DLLs behind, e.g.
>> * checking whether the namespace can be unloaded cleanly ... WARNING
>>   Unloading the namespace does not unload DLL
>> * checking loading without being on the library search path ... OK
>> For further details on my thoughts on this, see
>> https://github.com/HenrikBengtsson/Wishlist-for-R/issues/29.
>> Hope this helps
>> Henrik
>> On Tue, Sep 13, 2016 at 6:05 AM, Alexander Shenkin <ashenkin at ufl.edu>
>>> Hello all,
>>> I have a number of analyses that call bunches of sub-scripts, and in
>>> end, I get the "maximal number of DLLs reached" error.  This has
>been asked
>>> before (e.g.
>>> and the general answer is, "just clean up after yourself".
>>> Assuming there are no plans to raise this 100-DLL limit in the near
>>> my question becomes, what is best practice for cleaning up
>>> loaded packages in scripts, when those scripts are sometimes called
>>> other scripts?  One can detach all packages at the end of a script
>that were
>>> loaded at the beginning of the script.  However, if a package is
>required in
>>> a calling script, one should really make sure it hadn't been loaded
>prior to
>>> sub-script invocation before detaching it.
>>> I could write a custom function that pushes and pops package names
>from a
>>> global list, in order to keep track, but maybe there's a better way
>>> there...
>>> Thanks for any thoughts.
>>> Allie
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>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>PLEASE do read the posting guide
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